[v9 PATCH 1/2] PCI/ACPI: Support Microsoft's "DmaProperty"

[Joshua Peraza <jperaza@google.com>]

From: Rajat Jain <rajatja@google.com>

The "DmaProperty" is supported and currently documented and used by
Microsoft [link 1 below], to flag internal PCIe root ports that need
DMA protection [link 2 below]. We have discussed with them and reached
a common understanding that they shall change their MSDN documentation
to say that the same property can be used to protect any PCI device,
and not just internal PCIe root ports (since there is no point
introducing yet another property for arbitrary PCI devices). This helps
with security from internal devices that offer an attack surface for
DMA attacks (e.g. internal network devices).

Support DmaProperty to mark DMA from a PCI device as untrusted.

Link: [1] https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-internal-pcie-ports-accessible-to-users-and-requiring-dma-protection
Link: [2] https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
Signed-off-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Joshua Peraza <jperaza@google.com>
---
 drivers/acpi/property.c |  3 +++
 drivers/pci/pci-acpi.c  | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index 436019d96027..bb1459c43b6b 100644
--- a/drivers/acpi/property.c
+++ b/drivers/acpi/property.c
@@ -56,6 +56,9 @@ static const guid_t prp_guids[] = {
 	/* Storage device needs D3 GUID: 5025030f-842f-4ab4-a561-99a5189762d0 */
 	GUID_INIT(0x5025030f, 0x842f, 0x4ab4,
 		  0xa5, 0x61, 0x99, 0xa5, 0x18, 0x97, 0x62, 0xd0),
+	/* DmaProperty for PCI devices GUID: 70d24161-6dd5-4c9e-8070-705531292865 */
+	GUID_INIT(0x70d24161, 0x6dd5, 0x4c9e,
+		  0x80, 0x70, 0x70, 0x55, 0x31, 0x29, 0x28, 0x65),
 };
 
 /* ACPI _DSD data subnodes GUID [1]: dbb8e3e6-5886-4ba6-8795-1319f52a966b */
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index af370628e583..a457ae3e811a 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1438,12 +1438,34 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
 		dev->external_facing = 1;
 }
 
+static int pci_dev_has_dma_property(struct pci_dev *dev)
+{
+	struct acpi_device *adev;
+	const union acpi_object *obj;
+
+	adev = ACPI_COMPANION(&dev->dev);
+	if (!adev)
+		return 0;
+
+	/*
+	 * Property used by Microsoft Windows to enforce IOMMU DMA
+	 * protection from any device, that the system may not fully trust;
+	 * we'll honour it the same way.
+	 */
+	if (!acpi_dev_get_property(adev, "DmaProperty", ACPI_TYPE_INTEGER,
+				   &obj) && obj->integer.value == 1)
+		return 1;
+
+	return 0;
+}
+
 void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
 {
 	struct pci_dev *pci_dev = to_pci_dev(dev);
 
 	pci_acpi_optimize_delay(pci_dev, adev->handle);
 	pci_acpi_set_external_facing(pci_dev);
+	pci_dev->untrusted |= pci_dev_has_dma_property(pci_dev);
 	pci_acpi_add_edr_notifier(pci_dev);
 
 	pci_acpi_add_pm_notifier(adev, pci_dev);
-- 
2.48.1.601.g30ceb7b040-goog